Tire containing improved liner

ABSTRACT

Disclosed are vulcanized compositions of (1) from about 80% to about 99% of a rubber material selected from the group consisting of butyl rubber, halogenated butyl rubber having from about 1% to about 3% by weight of halogen and mixtures thereof, and (2) from about 1% to about 20% of a chlorinated hydrocarbon polymer having a chlorine content of from about 30% to about 70% by weight of chlorine, said composition having good impermeability to gases and tear resistance and being useful in tire inner tubes and inner liners.

This application is a division of application Ser. No. 715,326, filedMar. 25, 1985.

This invention relates to a composition of (1) a rubber materialselected from the group consisting of butyl rubber, halogenated butylrubber and mixtures thereof, and (2) chlorinated hydrocarbon polymercured with typical cross-linking agents having good impermeability togases, especially air, which is useful in tire inner tubes and innerliners, particularly in pneumatic tires having a vulcanized rubber linerply overlying all internal tire surfaces exposed in service topressurized gas.

Tire liners, based on blends of chlorobutyl rubber with a natural rubberor reclaimed butyl rubber or both, experience difficulty due todiffusion of gases, particularly air through the liner. In the past,epichlorohydrin rubber has been added to the aforementioned blends toimprove impermeability (U.S. Pat. No. 3,586,087). However, while thesetire liner compositions have good air impermeability, they do not have agood balance of scorch and physical properties.

This invention provides a vulcanized composition having goodimpermeability, i.e., resistance to gas or air diffusion and tearresistance, comprising, by weight of the composition, (1) from about 80%to about 99% of a rubber material selected from the group consisting ofbutyl rubber, halogenated butyl rubber having from about 1% to about 3%by weight of halogen, and mixtures thereof, and (2) from about 1% toabout 20% of a chlorinated hydrocarbon polymer having a chlorine contentof from about 30% to about 70% by weight of chlorine. The physicalproperties of the cured composition, such as adhesion to the tirecarcass, are not adversely affected by the addition of the chlorinatedrubber, yet the air impermeability and tear resistance are improved.

As is well known in the art, butyl rubber is a copolymer of from about95.5% to about 98.5% isobutylene and from about 1.5% to about 4.5%isoprene. Isoprene provides an unsaturated cure site for vulcanizingagents, such as the sulfur and zinc oxide system.

Halogenated butyl rubbers, useful in the practice of this invention,includes chlorobutyl, bromobutyl or blends of chlorobutyl and bromobutylrubbers, wherein the original unsaturation (usually from about 0.5 to3.0 mol. % isoprene residues) is largely maintained. A suitablycommercially available chlorobutyl rubber contains from about 1.1% toabout 1.35% by weight of chlorine and has a Mooney viscosity after 8minutes at 212° F. using the large (4-inch) rotor of 40 to 89 ML. Asatisfactory bromobutyl rubber prepared from a highly unsaturated butylrubber contains from 2.1 to 3.0% by weight of bromine, a density at 25°C. of about 0.96 g/cc, and evidences a Mooney viscosity at 212° F. of 40to 70 ML. The halogen in halogenated butyl rubber is present as a resultof post-treatment of the butyl rubber by reacting chlorine or brominewith the butyl rubber by methods known in the art.

The preferred rubber material for use in this invention is chlorinatedbutyl rubber.

The chlorinated hydrocarbon polymers useful in the practice of thisinvention include chlorinated polyisoprene rubber and chlorinatedpolyolefins.

Preferably, the chlorinated hydrocarbon polymers have a chlorine contentof from about 40% to about 66%, and most preferably from about 63% toabout 66%. Typically, the chlorinated hydrocarbon polymers have amolecular weight of about 50,000 to about 1,000,000 as determined bysize exclusion chromatography. Chlorinated polyisoprene having fromabout 63% to about 66% by weight chlorine is the preferred chlorinatedhydrocarbon polymer. Generally, the chlorinated hydrocarbon polymer ispresent in an amount, by weight of the composition, from about 1% toabout 20%, preferably from about 2% to about 10%.

Chlorinated polyisoprene and chlorinated polyolefins suitable for use inthe practice of this invention are commercially available.

The compatibility of the rubber material and chlorinated hydrocarbonpolymer is unexpected in view of the high amount of chlorine in and thepolarity of the chlorinated hydrocarbon polymer as compared to the lackof or extremely low amount of halogen and the nonpolarity or relativelyslight polarity of the rubber material.

Various amounts of crosslinking agents, accelerators or retarders, whichare the typical crosslinking systems used to vulcanize butyl rubber andhalobutyl rubber, can be added to the composition of this invention. Theoptimum amounts will depend upon the degree of crosslinking desired, thedegree of scorch safety desired, and the rate of cure desired. Thedetermination of the amounts to be used is well within the knowledge ofthose skilled in the art.

The crosslinker system can be formulated to cure through theunsaturation with typical sulfur cure systems with appropriateaccelerators, or nonsulfur crosslinking systems can be formulated tocure through the chlorine functionally with ethylene thiourea ordimercapto compounds, such as 2,5-dimercapto-1,3,4-thiadiazole,trithiocyanuric acid, dimercaptohydantoins or dimercaptotriazole with anappropriate base activator as set forth in U.S. Pat. No. 4,128,510 orU.S. Pat. No. 4,288,576, the disclosures of which are incorporatedherein by reference. Combinations of crosslinking systems can also beused such as, for example, mixtures of up to about 20 parts of asulfur/accelerator/ZnO sulfur cure package with up to about 10 parts ofa di- or tri-functional mercapto compound/Group Ia or IIa metal oxide,hydroxide or carbonate nonsulfur cure system.

In addition to the crosslinking agents, other ingredients commonly usedin rubber vulcanization can be used here also. For example, extenders,fillers, pigments, antioxidants, plasticizers, and softeners may beadded. The presence of a filler, particularly carbon black, while notnecessary, is beneficial.

The composition of this invention can be prepared by blending alldesired ingredients, except the crosslinking system, in any desiredfashion that allows intimate mixing, for example, in a Banbury mixer ortwo roll differential speed mill.

The crosslinking system comprising the crosslinking agent, oxides andaccelerators can then be incorporated or mixed with the blendedingredients in any desired fashion, such as by simply milling theblended ingredients and the crosslinking system on a conventional rubbermill. Uniform crosslinking is effected by heating at temperatures fromabout 140° C. to about 260° C. Other methods of mixing the crosslinkingsystem with the polymer will be apparent to those skilled in the art.

Crosslinking is effected at elevated temperatures. In general thecrosslinking temperature will be from about 140° C. to about 260° C.,preferably from about 150° C. to about 225° C., and most preferably fromabout 150° C. to about 205° C. The time will vary inversely with thetemperature and will range from about 5 seconds to 10 hours. Thecrosslinking temperatures and times are known to those skilled in theart.

The following examples set forth in the Table 1 illustrate theinvention. The control and the examples are prepared by the sameprocedure. All parts and percentages in this specification are by weightunless otherwise indicated.

                  TABLE 1                                                         ______________________________________                                                      Control, Examples,                                                            Parts by Wt.                                                                           Parts by Wt.                                           Ingredients     1          1       2    3                                     ______________________________________                                        Chlorobutyl rubber.sup.(a)                                                                    100        100     100  100                                   Chlorinated isoprene,                                                                         --         10      --   --                                    20% solution viscosity                                                        at 25° C. of 9-14 cps;                                                 64-65% chlorine content                                                       Chlorinated isoprene                                                                          --         --      10    2                                    20% solution viscosity                                                        at 25° C. of 17-25 cps;                                                64-65% chlorine content                                                       Carbon black     50        50      50    50                                   Stearic acid     1          1       1    1                                    Alkyl phenolic resin,                                                                          3          3       3    3                                    Ring and Ball s. pt. of 97° C.                                         Naphthenic oil.sup.(b)                                                                         8          8       8    8                                    Zinc oxide (ZnO)                                                                              3.0        3.0     3.0  3.0                                   Mercaptobenzo thiadiazole                                                                     1.5        1.5     1.5  1.5                                   disulfide                                                                     Sulfur          0.5        0.5     0.5  0.5                                   ______________________________________                                         .sup.(a) Chlorinated isopreneisobutylene copolymer, mol % unsaturation        ˜1.7%; ˜1.2% chlorine content; and 55 Mooney viscosity at         100° C.                                                                .sup.(b) Viscosity at 210° F., 30 (or is it 38) to 35 SUS units,       aniline pt. 168° F. to 179° F.                             

The properties of the cured vulcanizates of the examples and of thecontrol are set forth in Table 2.

                  TABLE 2                                                         ______________________________________                                        Properties of Cured                                                                          Control,   Examples,                                           Vulcanizate    Parts by Wt.                                                                             Parts by Wt.                                        (30 min. at 160° C.)                                                                  1          1      2     3                                      ______________________________________                                        Air Permeability.sup.(a)                                                                     2.86       2.03   2.57  2.62                                   (10.sup.-9 cm.sup.2 /sec-atm.)                                                Physical Properties.sup.(b)                                                   100% Modulus, psi                                                                            240         260   265   280                                    200% Modulus, psi                                                                            375         395   405   400                                    Tensile Strength, psi                                                                        1080       1020   1000  1030                                   % Elongation   900         850   860   870                                    Shore A Hardness                                                                              57         58     60    59                                    Tear Resistance, lbs/in.sup.(c)                                                               82         84     94    84                                    Adhesion to Tire Carcass.sup.(d)                                                              22         18     22    22                                    T-Peel lbs/in-pli                                                             ______________________________________                                         .sup.(a) ASTM D1434 at 25° C.                                          .sup.(b) ASTM D412.                                                           .sup.(c) ASTM 624 Trouser Test Specimen.                                      .sup.(d) Cured adhesion is measured by placing together a sheet (80 mil       thick) of the uncurd tire carcass compound with the crosslinking system       added and a sheet (80 mil) of uncured compounds of this invention on a        sheet of the control with crosslinking system added. A polyester film is      placed between the sheets at one end to provide a tab for pulling. Each       sheet is backed with a cloth sheet. The pad is placed in a mold about 160     mil deep. The pad is cured for 15 minutes at 182° C. Oneinch wide      strips  are cut and the peel adhesion is determined by measuring the forc     to pull apart the cured strips according to the procedures of ASTM D41838     The average of three pulls is reported.                                  

The tire carcass is typically natural rubber with other rubbers, such asstyrene-butadiene, added in lesser amounts and cured with a conventionalsulfur cure system.

Thus, this invention provides a vulcanized rubber composition having anunexpected reduction in air permeability which is a definite advantageespecially for products like tire inner tubes and tire inner linerswhere air retention is important.

The expression "consisting essentially of" as used in this specificationexcludes any unrecited substance at a concentration sufficient tosubstantially adversely affect the essential properties andcharacteristics of the composition of matter being defined, whilepermitting the presence of one or more unrecited substances atconcentrations insufficient to substantially adversely affect saidessential properties and characteristics.

Features, advantages and other specific embodiments of this inventionwill become readily apparent to those exercising ordinary skill in theart after reading the foregoing disclosures. In this regard, whilespecific embodiments of this invention have been described inconsiderable detail, variations and modifications of these embodimentscan be effected without departing from the spirit and scope of theinvention as disclosed and claimed.

What is claimed is:
 1. In a pneumatic tire, the improvement whichconsists of a vulcanized rubber liner ply overlying all internal tiresurfaces exposed in service to pressurized gas and comprising, asessential rubbery constituents, a composition consisting essentiallyof:(a) from about 80% to about 90% of a rubber material selected fromthe group consisting of butyl rubber, halobutyl rubber having from about1% to about 3% by weight of halogen, and mixtures thereof; and (b) fromabout 1% to about 20% chlorinated hydrocarbon polymer selected from thegroup consisting of chlorinated polyisoprene having a chlorine contentfrom about 63% to about 66% by weight and chlorinated polyolefins havinga chlorine content from about 30% to about 70% by weight.
 2. Thepneumatic tire of claim 1 wherein the rubber material is a halobutylrubber having from about 1% to about 3% by weight of the halogen.
 3. Thepneumatic tire of claim 2 wherein the halobutyl rubber is selected fromthe group consisting of chlorobutyl rubber, bromobutyl rubber andmixtures of chlorobutyl and bromobutyl rubber.
 4. The pneumatic tire ofclaim 2 wherein the halobutyl rubber is chlorobutyl rubber.
 5. Thepneumatic tire of claim 1 wherein the chlorinated hydrocarbon polymer ispresent in an amount from about 2% to about 10%.
 6. The pneumatic tireof claim 1 wherein the chlorinated hydrocarbon polymer is chlorinatedpolyisoprene.